318ti cranks like it has no compression

I hope the collective has some thoughts that I have missed. SWBO went out to start the 318ti yesterday and it sounded weird. It turned over very rapidly and would not start. I suspected that it had some how jumped cam timing but when I tore it apart today I found that was not the case. Did a quick and improper (engine was cold) compression test and got numbers in the 30-60 psi range. Car ran normally yesterday and I see no signs of mechanical catastrophe. Any thoughts?

dead ignition module

I had a car do that... the fiber cam gear had stripped, and the engine spun like there was zero load on the crank. The hint was seeing vapors going in and out of the carb. Thankfully for me it was a non-interference engine.

Did you crank it with the valve cover off? Were both cams turning?

I cranked it manually with a breaker bar with the cam cover off. I verified that the cams were turning and were correctly timed. It did sound just like a car cranking with a bad timing belt but the chain ect. seems to be where it should be. I'll look into the ignition module. Thanks for the input!

I'd take a closer look at the valvetrain based on those compression figures.

Did you hold the throttle fully open ?

The only thing that comes to mind is coil module.

However, as stated, those compression numbers don't look right.

Thanks for the suggestions! I neglected to keep the throttle open on the first test. I re-did it and everything was around 70 psi.

70 psi sounds kinda low for a M44... My M20 put up numbers close to (or more than) double that and even the 'down' cylinder was at 90.

Compression on that motor should be closer to 160-180

That's what I thought, but I wasn't sure how much difference doing the test with a cold engine would make.

I did both a hot and cold test on my M20 and while the numbers were slightly higher on average when hot, the difference was not substantial.

This ain't looking good

Did this thing run when you shut it off? Everything points to a real mechanical issue causing no compression but that's not something that just happens while it's sitting there in the driveway.

Perhaps the extra heat soak load pushed the head gasket out or something?

Timing chains and belts typically fail at startup or shutdown, due to the jerk of being accelerated from/to a stop.

I have to agree with the general opinion that it's likely a timing belt/chain failure. However I had a similar issue with a freshly rebuilt engine. I had somehow forgotten to remove a plastic cover from the intake manifold before I installed the carb. Drove myself nuts trying to figure out the issue. I know that this can't be the case with yours but is there any chance the butterfly is stuck closed or the intake is somehow obstructed? Mouse nest? Just a thought.

It ran normally last time it was out and hadn't sat for more than a day or two. I think it's time for the front cover to come off.

The next test I'd try if you can is a leak-down test.

Am I correct in assuming that all valves for a particular cylinder should be closed when that cylinder is at TDC?

Yes. Generally easiest to monitor with the valve cover off.

Entropyman wrote: Am I correct in assuming that all valves for a particular cylinder should be closed when that cylinder is at TDC?

TDC happens twice for every complete cycle of a four-cycle engine. so TDC firing should have all valves closed for the cylinder that's firing. TDC exhaust will have exhaust valves open.

Well, Angry Corvair was correct. The coil was bad. Apparently the low compression was caused by unburned fuel "washing down" the cylinder. It had to crank for a while with the new coil but it finally caught and runs great now! Thanks to everyone for their help and input!

wonderful news.

Wow, that's a fantastic outcome. Congrats